Method for reactive sputter deposition of a magnesium oxide (MgO) tunnel barrier in a magnetic tunnel junction

Abstract

As part of the fabrication of a magnetic tunnel junction (MTJ), a magnesium oxide (MgO) tunnel barrier is reactively sputter deposited from a Mg target in the presence of reactive oxygen gas (O 2 ) in the “high-voltage” state to assure that deposition occurs with the Mg target in its metallic mode, i.e., no or minimal oxidation. Because the metallic mode of the Mg target has a finite lifetime, a set of O 2 flow rates and associated sputter deposition times are established, with each flow rate and deposition time assuring that deposition occurs with the Mg target in the metallic mode and resulting in a known tunnel barrier thickness. The commencement of undesirable Mg target oxidation is associated with a decrease in target voltage, so the sputtering can also be terminated by monitoring the target voltage and terminating application of power to the target when the voltage reaches a predetermined value.

1 . A method for reactive sputter deposition of a magnesium oxide (MgO) film on an iron-containing film in a sputter deposition chamber comprising: 
 providing in the chamber a sputtering target consisting essentially of Mg and a substrate on which the iron-containing film is formed;    applying power to the target to sputter deposit Mg atoms onto the walls of the chamber while the iron-containing film is protected from exposure to the sputtered Mg atoms;    introducing O 2  gas into the chamber at a known flow rate;    exposing the iron-containing film to reactively deposit MgO onto the iron-containing film; and    continuing the reactive deposition for a period of time, said time period and known flow rate selected to assure minimal oxidation of the target.    
     
     
         2 . The method of  claim 1  further comprising, prior to applying a voltage to the target to sputter deposit Mg atoms onto the walls of the chamber, applying power to the target in the presence of an inert gas to thereby substantially remove oxygen from the surface of the target.  
     
     
         3 . The method of  claim 2  wherein the inert gas is argon.  
     
     
         4 . The method of  claim 1  further comprising, prior to applying power to the target to sputter deposit Mg atoms onto the walls of the chamber, etching the surface of the iron-containing film.  
     
     
         5 . The method of  claim 1  further comprising, after reactive deposition for said time period, exposing the deposited MgO film to O 2  in the chamber.  
     
     
         6 . The method of  claim 1  wherein continuing the reactive deposition for a period of time comprises terminating application of power to the target when the target voltage reaches a predetermined value.  
     
     
         7 . The method of  claim 1  further comprising, prior to applying power to the target to sputter deposit Mg atoms onto the walls of the chamber, determining a set of known O 2  gas flow rates and associated time periods.  
     
     
         8 . The method of  claim 7  wherein determining said set comprises applying power to the target and, for each known flow rate in the set, measuring the decrease in the target voltage with time.  
     
     
         9 . The method of  claim 1  wherein, as a result of the reactive deposition a MgO film has been deposited to a first thickness on the iron-containing film, and further comprising repeating the method of  claim 1  to thereby increase said thickness.  
     
     
         10 . The method of  claim 1  wherein the iron-containing film is an alloy comprising cobalt (Co) and iron (Fe).  
     
     
         11 . A method for fabricating a magnetic tunnel junction on a substrate in a sputter deposition chamber comprising: 
 depositing a first iron-containing film on the substrate;    covering the iron-containing film with a shutter;    applying power to a sputtering target consisting essentially of magnesium (Mg) to sputter deposit Mg atoms onto the walls of the chamber while the iron-containing film is protected by the shutter from exposure to the sputtered Mg atoms;    introducing O 2  gas into the chamber at a known flow rate;    removing the shutter from the iron-containing film to reactively deposit a MgO film onto the iron-containing film;    continuing the reactive deposition for a period of time, said time period and known flow rate selected to assure minimal oxidation of the target; and    depositing a second iron-containing film directly on the MgO film.    
     
     
         12 . The method of  claim 11  further comprising, prior to applying power to the target to sputter deposit Mg atoms onto the walls of the chamber, applying power to the target in the presence of an inert gas while the target is covered with a shutter to thereby substantially remove oxygen from the surface of the target.  
     
     
         13 . The method of  claim 12  wherein the inert gas is argon.  
     
     
         14 . The method of  claim 11  further comprising, prior to applying power to the target to sputter deposit Mg atoms onto the walls of the chamber, etching the surface of the first iron-containing film.  
     
     
         15 . The method of  claim 11  further comprising, after reactive deposition for said time period and prior to deposition of the second iron-containing film, exposing the deposited MgO film to O 2  in the chamber.  
     
     
         16 . The method of  claim 11  wherein continuing the reactive deposition for a period of time comprises terminating application of power to the target when the target voltage reaches a predetermined value.  
     
     
         17 . The method of  claim 11  further comprising, prior to applying a power to the target to sputter deposit Mg atoms onto the walls of the chamber, determining a set of known O 2  gas flow rates and associated time periods.  
     
     
         18 . The method of  claim 17  wherein determining said set comprises applying power to the target and, for each known flow rate in the set, measuring the decrease in the target voltage with time.  
     
     
         19 . The method of  claim 11  wherein, as a result of the reactive deposition a MgO film has been deposited to a first thickness on the first iron-containing film, and further comprising repeating the method of  claim 1  to thereby increase said thickness.  
     
     
         20 . The method of  claim 11  wherein the first iron-containing film is an alloy comprising cobalt (Co) and iron (Fe).  
     
     
         21 . The method of  claim 11  wherein the second iron-containing film is an alloy comprising cobalt (Co) and iron (Fe).  
     
     
         22 . The method of  claim 11  wherein the magnetic tunnel junction is part of a magnetic tunnel junction read head.  
     
     
         23 . The method of  claim 11  wherein the magnetic tunnel junction is part of a magnetic tunnel junction memory cell.  
     
     
         24 . The method of  claim 11  wherein the magnetic tunnel junction is part of a magnetic tunnel transistor.